Increasing mobility and spin lifetime with shear strain in thin silicon films

Because of an ongoing shift to FinFETs/ultra-thin body SOI based devices for the 22nm node and beyond, mobility enhancement in such structures is an important issue. Stress engineering used by the semiconductor industry to boost mobility was predicted to become less efficient in ultra-thin SOI structures due to the less pronounced dependence of the transport effective mass on strain. Using the k · p Hamiltonian which accurately describes the wave functions of electrons in silicon in the presence of strain and spin-orbit interaction, we show that the wave functions and the matrix elements' dependences on strain compensate the weaker dependence of the effective mass, which results in an almost two-fold mobility increase even in ultra-thin (001) SOI films under tensile [110] stress. In addition, we demonstrate that the spin relaxation rate due to surface roughness and phonon scattering is also efficiently suppressed by an order of magnitude by applying tensile stress, which makes SOI structures attractive for spin-driven applications.